The polybrominated biphenyls (PBBs) and polychlorinated biphenyls (PCBs) are inducers of hepatic mixed-function oxidase. The purpose of this study is to determine the structure-activity relationships of PBB isomers and other component of the commercial PBB mixtures, as inducers of cytochromes P-450 and P-450 and to relate these effects to toxicity.